Picked up the Set in South-Eastern Ohio on Friday, and have just gotten it back home to South-Eastern PA.

Other than some dry rotted insulation, and a heap of dust, the set looks pretty decent for 59 years old.

'As is' Pictures attached. (The modern cartridge fuse holder is my own temporary addition). The cabinet is in reasonably good shape, save the one tear in the veneer. It looks better in person, the water spots are on my lens, not the cabinet!

The front and rear access panes for the HV cage are completely missing, so I'll have to machine some new ones-- but that's for another time...
More to follow!

Alex

That's one of the harder models to come by. Congrats are in order.That cabinet style according to RCA was "Moderne".
I may have a rusty door for your cage.It could be cleaned, and, re painted the original flat balack. If this set has the un painted cage, that will work, too. Pm me if interested. Cagee door free. Shipping charges, and, pro. packing by ship, and, pack is all I want. I'll make nothing on this.I just wish to help.
Bill Cahill

Alex, welcome to the forum and to the wonderful world of vintage TV restoration. Please keep us all posted on you restoration progress. For you electrolytic twist-loc cans, you may want to consider the brand new manufacture cans offered by Antique Electronic Supply. They are not cheap, but a good alternative to restuffing.

I would like to see anything you have on early color TV, as that is my primary interest these days.

And don't hesitate to ask questions and post comments, that what the forum is for. We ARE interested. Have fun!

If you're curious what it might take to restuff those cans, check this thread out: http://www.audiokarma.org/forums/showthread.php?t=231914&page=2

Looks like a fun set to work on. Good luck!

That was a great thread, thanks. Got the chassis about half cleaned up last night, I'll post some more pictures once I start recapping.

Got the chassis relatively clean, top side. And dove into 'the works'.

I had previously heat shrunk some tubing over the leads of the main transformer, but the cotton an rubber was still causing issues, flaking off at the 'mouth' of the transformer and doing it's best to short out. I decided to pull open the transformer, remove the original leads, and solder new leads directly on the windings. Where I couldn't get adequate access to the windings, I cut the original lead as short as possible, and heat shrunk the new connection. It turned out okay! I'll post pictures when I get it back together.

I also took out the first twist lock cap, and began the restuffing process. Boy does it take a lot of heat to wick up solder off the chassis connections! I'm used to working with 0402 SMT parts under a magnifying glass -- so this is quite a change.

When I finally got the cap out, I went the dremel route, and created tabs to pull back. However the 'Pull out the terminals and fiber disc and save it,' part didn't go so hot. Even with a lot of heat, the terminals and disc refused to let go from the innards. Eventually I broke the disk by pulling on it, so I'll have to make a new one out of phenolic. Any other tips for better success??

With the disc out, I finally was able to stab some pliers into the can, reheat, and pull the works out. Ive got the new capacitor assemblies ready to go, as soon as I make a new insulator disc. The process is a ton of work, I can understand why people would just put the new caps under the chassis.

Other than that, I just started replacing some caps and resistors -- almost all that I have checked, even the lower valued ones, are out of tolerance.

Once the power supply and other electrolytics are replaced, and new tubes are in, do you generally find that it is relatively safe to attempt to fire up the set? Or is it always advisable to replace all the paper caps first? I have read that people have success with the 'replace a few and test' method.

Any help appreciated as always,
Alex

Alex, I usually just cut the can off right above the step, this leaves the Phenolic intact, then I drill some very tiny holes near each leg for the + leg of the new cap to go through, tie them all together on top and drill one more hole for the ground wire to pass through, glue the can back on with JB weld.

If the can is Hacksaw accessible you can do this without even removing it from the chassis, you do have to be careful not to bust the Phenolic mounting wafers when you do it that way.

Sometimes you can't get all 3 or 4 new caps inside the can, in that case I just put the remaining one under the chassis connected to the lugs.

Hi Alex,

Seems like a good night for stuffing caps :) I've been using a slight variation of the technique you used. I open up the can and removing the steel ring like you've done. Then, I heat up the can with the wafer and pins in place. A slow, steady twist & pull with pliers on the pins and viola the whole slug comes out. Finally, I unrolled the aluminum and goop to free up the pins. This way the entire base is in great condition.

I like Eric's technique too. A pipe cutter can make quick work of the aluminum can. It's especially nice when the cap is in a cardboard sleeve.

Good luck,
Bob

No, not safe to try now. Especially with those black beuties in there, and, in hv cage.
Not advisable.
Where origninals are 1,00 volt, use at least that high voltage, as they have quite a pulse on them. Cap values on damper, and, yoke circuits are fairly crittical, and, disc caps will not work properly. Especially not on vertical circuit.
Clean hv thoroughly, as there is tendency to arc.
Yokes, and, flybacks are prone to failure in these sets, are as vertical oscilator transformers.
I do with out line caps, and, line resistors as without them set chassis is electrically safer to touch.
They stopped noise such as car generators, and, diathermy machines, which we no longer use.
Bill Cahill

Thanks for the input,

I'll take a stab at the heat and twist method on the next twist lock.

I have access to a wide array of HV capacitors, so getting 1kV 5% Films in just about any value isn't a big problem. I'll ohm out, and hipot test the Flyback and vertical oscillator trans. before firing the set up for the first time.

As for the line caps and line resistor, my work in the power electronics industry tells me that the line caps are there as much for RFI suppression from the set out to the world, as for the world into the set. Without them I imagine you could get some local oscillator noise out onto the line which would interfere with other sets. However, I doubt the single order filter really works any miracles -- modern RFI filters are quite an artform in themselves! I'll put in new Y2 safety grade ceramics. I have an isolation transformer at my disposal as well.

I was replacing caps around the vertical oscillator, and something didn't look quite right --My first schematic change!

Sam's shows the vertical oscillator as a 6J5, where as the RCA chart in the cabinet shows the 6SN7 Dual Version. 1/2 of the 6SN7 is connected exactly as the 6J5 would be, with the other 1/2 pulling duty as the synch amp, where sams shows 1/2 12AU7. The 6SN7 is biased differently than what is shown on the 12AU7, but I guess that is to be expected.

Things get even weirder upstream of that at the DC-Restore/Synch Sep tube, where my chassis bears little resemblance to the Sams schematic. There appear to be both halves of a 12AU7 interconnected up there, where sams shows only 1/2.

I haven't fully traced out that schematic yet, but if I get time, i'll do my best to plot it out.

For what its worth, my Sam's guide for the 6T75 shows chassis KCS47, A; where the actual unit is stamped KCS47AT. Does anybody have this particular schematic? Right now i'm pretty much operating on the 'Blindly replace what is there' technique with no schematic of some sections.

Other than that, a few pics of the re-leaded transformer. Luckily wire is available in all colors under the sun!

Alex

Send me an email address and I will send you the schematic.

Great job on rewiring the transformer!!

Well, here it is a week later, and I really went to town on cap replacement. And, with many thanks to John, I now have a (more or less) accurate schematic of the AT chassis. Incidentally, I have come across several 'missing' components in the IF section. There has been at least one omitted capacitor that should be in parallel with an inductance to form one of the traps -- my guess is that this was not a design change, but an error in the original construction. So far I haven't put it in -- we'll see what falls out.

I'm about 90% done with all the paper caps, I am leaving all the mica's in place at the moment. And, I have one of the 3 electrolytic twist locks bodged back in. For now, I've givin up on restuffing them -- I'll worry about authenticity later -- right now I'm still in the 'new project euphoria' stage, and want to get the set up and running.

Current state of the chassis is shown -- Mylar is my capacitor brand of choice -- but there's some Panasonic, Vishay, and a little SBE in there, too.

Incidentally, how in the world do you guys clean the underside of the chassis? When I get a group of caps removed, I clean what I can of the underside of the metal, but even the wiring is completely coated in 'goo.' I dare not use alcohol to clean it, as I fear it will brittle the aging plastics. This set was picked up in major coal country, -- maybe it just lived a dirtly life.

As the crow flies, this was picked up about 80 miles from the Columbus Oh TV market, and also about 80 miles from Charleston, WV. I'm suprised there was anything on the air in 1950...

If I can keep it up a little while longer, I think I'll be ready to bring it up on a variac next weekend. And then, either great exhilaration or mild depression will result :)

Alex

Alex, which inductor has the missing capacitor? As for cleaning, other than a good dusting with an air compressor, I don't try to clean the underside of chassis. The underside of your chassis looks pretty clean to me.

When I bother cleaning the underside, I use odorless mineral spirits and q-tips.

Great job! Your set looks nice! Like I said in my thread, a lot of those cans are made slightly different at the terminal end,(difference in disc material and the way the metal edge is knurled over) my method was used on mid 60s caps in a few Zeniths and an Admiral round color set. Terminals and fiber disc came right out every time. I'll have to try the cut the can off while on the chassis method myself, if I can get into a set with enough room to do so, hasn't happened yet. The Motorola I did used a very annoying material for the disc and almost all of the terminal was aluminum so I had to bring the leads outside of the cap and hide them.

Wow -- a CTC-4, very impressive! Very nice page.

John, the missing parts Ive identified are as follows, using reference designators from the schematic you gave me for the AT chassis:

C131 -- 47pF in the 1&2 video amplifier at the 4.5MHz trap. (Sorry, just can't force myself to say mega cycle!)

The second/third seem less critical, but:

C220 -- 100pF
C219 -- 0.0015uF both in the cathode circuit of the 1st video amplifier

Alex

Alex, while I am not much for those nFarads, I am a Hertzian kinda guy. :-). Hard to know if those were just omissions, or production changes. RCA seemed to be in constant flux with the design of this set. I would try tuning the trap, and if it won't null at 4.5mhz, I would put the cap back. I would probably try the other missing caps after I got the set working and see what difference (if any) they make. Good luck, thanks for keepin' us posted.

Well -- that's it for the Film Cap replacements -- save the Caps in the Damper circuit, and a few other 1kV parts that I had to order.

Other than that, its on to the electrolytics.

Alex

Anybody have any tips for removing rusty tube shields from their tubes?

I have a few that won't give up the fight...

I've pried tube shields off in the past - of course those were the shields that were made of spring metal that just met or overlapped on one side. If they're solid, I'd try dripping a bit of Liquid Wrench or Maltby's on the tube and letting it sit for a few days. You may lose the markings though.

I push them through with a nut driver over the tip, a little lube might help as mentioned.

How did I miss this thread? Great set and congratulations.

That is the exact same chassis in my TV. I'm really having a lot of problems getting mine going.

http://www.audiokarma.org/forums/showthread.php?t=226988

Thanks for the tips -- Sansuii, you're way ahead of me in performance at this point!

Well, the set has now consumed 90% of my free time for 2 weeks, but I finished recapping the last 5 or 6 films, and all the electrolytics. I guess this is where the real fun begins...

I haven't removed the CRT or the speaker, nor have I made any long wiring harnesses yet, so I put the chassis back in the set, and brought it up slowly on the poor man's variac -- assorted series light bulbs, while monitoring the 375V Bus, as its the only one readily accessible on the picture tube when the chassis is in.

Once I got it up to full line, there was still not much going on, Not so much as static on the speaker. The 375V bus topped out at about 445VDC, seemingly indicating that there's an awful lot of something not drawing very much current. (incidentally, I have gone through most of the resistors I deemed critical -- the power supply chain seemed to check out reasonably well). I flipped the audio input switch to Phono, and hooked up an IPOD on an RCA cable. Still Nada.

Peering inside, it looked like the 6K6 audio output tube was showing some haze, like it might have gone gassy. So much for NOS. I poked around, but all I could come up with was a 6V6 -- close enough to try. I popped it in, and Voila! Sound. Albeit pretty faint, even at top volume. After some more digging, I did find another 6K6, and put it in. Moderately better results -- for about the next 25 seconds when the 5U4 gave up the ghost.

I can see right away that I should have stocked up about 5X more on all the tubes. So. There it is. No signs of raster, no signs of HV. Either that or the CRT is dead. The only up side is that the CRT filament is definitely not open.

I'd consider bringing the set up on silicon diodes at reduced line voltage to get the proper bus, but the death of the 5U4 seems to indicate something is pretty wrong. Plus, the filament voltages would be low. When I get some more 5U4's, I'll start by digging into the other bus voltages.

When you guys probe on a bench, do you always do it with the CRT attached? I was thinking of jumping out the CRT 'loopback' pins on the power supply, and just pulling the horizonal output tube to start looking at things. Whats your standard procedures?

Guess I'm taking hte weekend off, since new 5u4's wont get here for a few days.

Alex

Alex, it seems odd that you would have 445 volts of B+ if there was a short, did the heaters on the 5U4 burn out?

It's a bit late to point this out now but I never recap an entire set all at once any more, there are too many chances to make a mistake. I usually do the main filter cap first and then try it, then if everything is OK I proceed to the next one.

Well any way lets work on what you have, it might be a good idea to use diodes and a 200 watt dim bulb tester while you check things out, it will keep you from having to replace any more 5U4's if there is a problem.

I'd look closely to make sure you haven't wired any electrolytics in backwards, if you have it'll soon show itself in any case when it vents.

There is a 5" CRT used for testing purposes, 5AXP4 I think it is, they show up on eBay now and then.

You don't have to hook up the CRT at all, you can leave the chassis out of the cabinet with the HV lead inside a glass jar to keep it from arcing, this will allow you to do some voltage checks and concentrate on getting your high voltage working.

I'm not sure what you mean by "loopback" pins? you should be able to just leave the CRT base connector unplugged while you work on it, it's not a series string chassis right?

Might be a long shot , but also check the transformer for shorts between the 5 volts windings and the B+ windings , the 445 volts is a bit interesting .
Could there be a missconnection when you changed the transformer wires ?

I have been working on mine on the bench without CRT. You need to jump across two pins on the yoke connector to feed power to the rest of the set. I'm on vacation next week and will try to work on the set and post results.

Does that mean that you were testing it without the yoke connected?
John

Lot of questions in there! Let me try to answer:

Replacing caps piece meal was my first thought, but I got some advice in the forum to go ahead and recap the whole thing. Its neither here nor there -- The set showed no signs of life before recapping, even though the electrolytics weren't totally shot.

1) No Reverse Polarity electrolytics
2)Yes, it seems unlikely there is a short on B+ with 475V. In fact w/ 355V center tap on the 5u4, the peak open circuit voltage is only 500ish. So there's very little drop going on. Im not sure what went in the 5u4, i'll check tonight.

3)The CRT base connector on this set has 2 pins which do nothing but connect the filter choke to the rectifier when the connector is inserted. Ie. if you do nothing, the power supply is completely disconnected downstream of the rectifier.

4)Tube TV -- I'm a little confused -- the 5V winding for the 5u4 filament IS the b+ winding. Maybe I mis-interpreted what you're asking. In any case, with everything else disconnected, all the transformer windigns show isolation.

5)I'll try to bring the set up w/ a pair of diodes and a variac. However, since the diodes will drop much less voltage than the 5u4, i'll have to keep the line voltage low. This will also lower the 6.3V filament taps. Need I be concerned?

Solid state switch mode power supplies are my main game, so I'm still getting used to the tube side of things...
I'll poke around some this weekend and see what I can see.

Alex

Diodes are a no go. The hv will not work below 100-110v ac input.
The picture tube socket isn't the connector to B+. It's two pins on the yoke socket.
This set should be operating at 387v dc on rectifier under full load at a line voltage of 117 volts ac.
Your present dc is way high... Do you have the yoke plugged in?
Also, disconnecting the speaker plug saves the audio out from dammage because it removes the voltage from both the plate, and, screen. However, the more circuits not functionning, the higher your power supply voltage will be.
Also, that single secion boost filter is important. If open, or, shorted, that kills the vertical, and, damper circuits.
Just completely re-cap it.
And, oh, yes. Those 1kv capacitors on audio out., vertical, yoke, horiz. out., and, damper circuits are very important.
Black beuty caps are no good, either.
Get rid of your line caps, and, resistor if you want real relative safety.
The RF it isolated set from is rarely produced anymore.
Cars now run on alternators. Not generators.
And, who uses a diathermy machine anymore?
No real noticable change in rf in signal without the line caps.
I have alot of experience on these sets, so, if you need my help, please feel free to pm, or, e mail me.
Bill Cahill

Yes, I know the b+ is on the yoke, and yes it was connected. I meant CRT connector as a generic term.

If the power line choke were open, I'd get no voltage on B+ at the CRT.

The entire set is recapped.

What makes you say diodes are a no go? The HV shouldn't care what the line voltage is, as long as the DC voltages come up correct.

If you're making the argument that the powerline is cleaner now than in 1950, I'll disagree -- ask the guy who works switch mode supplies! :) Just try running a flourescent light on the same outlet...

I didn't mean that to be Smart Alec-y :) Not sure if it came off that way!!

Well, you did. That's exactly why I rarely come here.
I offer help, and, I'm treated as if I know nothing.
I wanted to help you. That's all.
Good luck with the set.
B C

I have much to learn from everybody's experience with this set, and I welcome and enjoy reading everybody's comments. Thanks for following as I muddle through this.

The engineer in me systematically responds to questions and suggestions. No cold shoulders intended.

I am geniuinely curiuos to know if there is a reason I shouldn't attempt to diode across the rectifier tube -- However, the suggestion to recap specific sections confuses me, as my last post explains that it has already been done. Paper caps, and black beauties included.

Sorry , my error on the 5V winding .....

I was merely warning about voltages of certain caps. I believe is doing the entire thing first.
The rectifier isn't your problem. The set obviously isn't drawing any current.
I'd start looking for open, or, way off value resistors in B+ Supply, and, to each section of the set. This is a major weak point on these sets.
This set should operate at 387 volts at 117 volts ac.
You said, I think, you were getting 488 volts?
That's clearly NOT a rectifier problem.
TV isn't getting out of surge mode.
Check B+ voltages on all major circuits, such as vert. oscilatro, vert. out. caution, don't try to measure plate of output tube, damper, or, plates of horiz. output, hv rect. tubes.
There is a dangerously high ac component there.
The boost filter negative leade connects to cathode of vertical output tube.
Check the .25A fuse in hv cage to make sure it isn't blown.
The correct value of that fuse is .25A 250volt slo blo.

Yoke failures were common then. If horiz. winding shorts enough your hv will fail.
Did you replace all the paper caps in hv cage, also?
There are 4. Two on yoke, and, two on damper.


I've had alot of resistor failures in these sets. They either open, or, go 100 percent, or, more, off value.
Anything above 20 percent should be replaced.
Bill C

Yes, I know the b+ is on the yoke, and yes it was connected. I meant CRT connector as a generic term.

If the power line choke were open, I'd get no voltage on B+ at the CRT.

The entire set is recapped.

What makes you say diodes are a no go? The HV shouldn't care what the line voltage is, as long as the DC voltages come up correct.

If you're making the argument that the powerline is cleaner now than in 1950, I'll disagree -- ask the guy who works switch mode supplies! :) Just try running a flourescent light on the same outlet...

I'm still confused about the jumper then. If you had the yoke connected why did you need a jumper?

John

The jumper is original to the set. It's a disconnect in case yoke is accidentally un-plugged.
That cuts all b+ to set.
iF HIS AC line was open, nothing would work. His tubes are lighting, and, he has B+. The problem is more like the set, or, at least part of it, isn't drawing any current.
I still say resistors are likely at fault.
Bill C

Hi John -- I was asking about using a jumper when checking things on the bench without the yoke connected. You're right, w/ the yoke connected there is no need.

Bill was right on the money with this one.

The 4k Resistor between 375 and 220V is bad - it reads okay at room temp, but reads close to open if you measure soon after power down. How's that for a positive temperature coeffecient. Fun.

The filament went on the original 5U4 -- but I've double checked isolation between the filament windings and all the other taps -- no problems. The open circuit AC voltage across the 5U4 filament is 5.1. Not sure why things went wrong.

Incidentally, I decided to go for the diode route instead of another 5u4 for now. Since the 5u4 drops somewhere around 40Vpeak at full load, I ball-parked some series resistance (220 Ohm 5 W) for each diode in the full wave rectifier. This turned out to be pretty dang close.

With a bunch of parallel 50k 1W resistors bodged in for now where the 4k Power resistor should be, I finally pulled the variac out of storage, and brought the set up slowly. The 370V BUS leveled out at 381, the 200V BUS at 195, and the 125V Bus at 81V. Can't win 'em all. One of the series resistors is high -- I'll get to it later.

At this point, I could hear the vertical output transformer rev-up!

I put the chassis back into the cabinet, and hooked up an aux audio input, -- sound! Not bad for how far off the biasing is due to the 125V BUS. The 6k6 audio output tube has an interesting blue glow....
At this point, there was still no sign of any HV -- I suspect the horizonal output tube, who's getter flash now looks suspiciously oxidized. I'm not having the greatest of luck with ebay'ed tubes!

Back to the bench, and an oscilloscope.

1st capture is 370V Bus Ripple voltage AC coupled at 10V/division. Ripple is about 4Vpp -- I'll take that!

2nd capture is the vertical drive at the grid of vertical sweep output tube. Looks reasonable, stable, and linear!

3rd capture is Tap C of the horizontal oscillator transformer. Gotta admit, i'm not exactly sure what waveshape I should capture here, but the general frequency is about right - about the 15kHz ballpark, although it's not particularly stable.

That's it for now -- all of the about captures are free running oscillators with no video or RF applied.

Is there anything specific I should check out before some new 6BG6 horizonal output tubes arrive?

Any tips, thoughts or comments appreciated

Alex

Congratulations on the progress! Yeah, Bill has the experience to know and his suggestions are good.

Due to the ambiguities the English language sometimes presents us with I wasn't sure that you weren't testing with the yoke disconnected. That seemed like it would have been a bad thing to me and could have caused the high readings.

Resistors that change like that can be a real pain.

John

First, without the yoke, you can't get hv.
Secondly, the correct horiz. freq. on these sets is 15,750.
Yours sounds very low.
The 5U4 is quite capable of getting up the proper voltage as long as the tube is good. And, a tube tester claiming it's good means very little.
If the getter on horiz. out. has changed from clear, it's likely gassy. Not a good thing.
Blue glow on aud. out. is gas. Also not good.
The micas in these sets tend to get leaky, and, will cause nasty things in picture.
In the horiz. the oscilator will not run on correct frequency, and, could have a hunting problem.
In sync circuit, it will make both the vertical, and, horiz. un stable.

Which chassis is this?
Does it have the 6J5 vertical oscilator, or, the 6SN7 vertical oscilator-sync seperator?
If it is the later more deluxe set, there are other things you need to know that sams doesn't include.
The tube chart in cabinet will help there.
Also, if there is a 3 lug terminal strip screwed to the side of chassis near vert. oscilator, it's the more deluxe chassis. They primarily use it with a capacitor going to it.
It's a coupling cap not used on cheaper chassis.

There is a 100 ohm two watt resistor on horiz. out. Cathode that will likely need replacement, as well. They take alot of current, and, tend to cook, causing them to go 50-100 percent high.
That will also affect your hv.
Bill C.

Hey Bill,

A lot of these questions were answered a few posts ago, but here goes:

When I made the comment about no HV, the chassis was installed in the cabinet, and the yoke attached. No issue there.

I know that horizonal line freq is 15,750, unfortunately I have no really accurate way of measuring. All I have is an out of calibration 20Mhz Analog scope. So saying '15kHz ballpark' is about as accurate as I can get without the timebase being re-calibrated.

Thanks for the tip about the mica's, they're on my 'watch list' when I get there.

A few posts ago, I noted this was the 6SN7 vertical oscillator - sync separator. John was kind enough to give me the proper schematic, as my Sams shows the 6J5.

This set has a 2 lug terminal strip in the location you indicate -- I think it shows in 'recapped' pictures.

The 100 Ohm in the cathode section WAS bad. It is now a 2W Metal Oxide resistor. Its the blue one up there in that tightly crammed corner of the chassis.


For what its worth, I'm trying to hunt down the sagging 120V BUS problem -- my original comment of a resistor being high was based on an incorrect glance at the schematic.
My set does not have the multiple parallel resistors between the busses in the power supply, but instead has single wirewound power resistors in each of these locations. Not sure if this is original, or a replacement. I went through the academic exercise of calculating the 'expected' equivalent resistances from point to point in the power supply based on the parallel resistances in that section, as well as the 'tie' between 120 and 370 that feeds the RF Amplifier. Below is what I got...nothing seems off by more than ~ 20%:

370 to 250: Calculate 3.65k, measure 3.77k
370 to 120: Calculate 11k, measure 10.6k
250 to 120: Calculate 10.9k, measure 10.2k
120 to Com: Calculate 4.28k, measure 3.8k -- this is off about 12% and could pull both 120 and 250 low, but doesn't account for the full difference.

Can anybody confirm these measurements on another chassis?
Alex

I don't believe you looked in all the right places.
Manny circuits, and, resistors can cause troubles.
I F b+ resistors, All audio resistors, tuner b+ resistors,
B+ resistors in video amp, Sync, vert. oscilator, even to a degree, the agc circuit.
I didn't seee all the posts, so, sorry, I wasn't aware of the earlier information.
Try removing he hv doorknob cap, and, trying set without it. Any higher hv?
If so, the doorknob is bad.
They simply snap in, and, out of clamps.
Be sure of direction it comes out. Even mica seems to develop a memory.
The hv doorknob is mica.
They have been known to fail.
It's 500pf 20kv.
If you need to, you could live without it.
Just not as good hv filtering. But, they are obtainable.
Bill Cahill

I'll make the blanket statement that any resistor that shared a node with a paper or black beauty cap was taken out of ckt, measured, and replaced if grossly out of tolerance.

So that leaves mainly the IF and tuner sections unchecked at this point. I'll look there.

What about resistors to screens, plates, tuner, plate of audio amp, cathode of audio output, etc.?
A blanket statement like that just isn't enough.
Come on. You're a designer... Think. Look at the repair end of things. There are many resistors that can be bad. Also, it's very common for hv rect., and, or, hv cap to short.
And, tube testers won't show shorts because the voltage applied is only a very small protion of the tube's operational voltage.
Same with 5U4's.
Bill Cahill

For what it's worth, I came up w/ a way to align the horizontal oscillator frequency without yet having any NTSC sync pulses from the detector stage to use:

I used my computer soundcard to output a 15734Hz sine wave (went for the color standard, not sure why), and used this to trigger my scope. Then I brought in the horizontal on the 2nd channel, and turned the slug until it synchronized. After that, I adjusted the sine wave slug for equal peaks as shown in Sams. However, I ran out of adjustment just before the peaks equalized. At least it's stable now.

Have a little bit of faith in me, here, Bill!

The blanket statement immediately lets you know what I have and have not checked. I haven't gotten to everything yet.

Plate, Cathode, screen and grid of audio amp and audio output - Yes. Checked. These all shared tie points with new film caps and were measured.

The same is not true of resistors in the tuner and IF sections, because I haven't had anything out of circuit there yet. All in due time, but thanks for pointing me to keep looking there.

Well, with the horizontal running well, I hoped to have HV, but no such luck. All the biasing on the HOT looks pretty reasonable. With John's troubleshooting help, I tried the 'arc to a screwdriver' trick on the cap of the HOT and the cap of the 1B3.

Nothing going on the HOT, but I can pull a small arc from the 1B3. That gives me even more faith that the flyback is good. No change when I pull the HV cap. Here's hoping all goes well with a new 6BG6 HOT. I should know something more in a few days.

In the mean time, I put some video on Chan 3, and followed through the Tuner, IF, and amplifier stages. I had video at the Detector, but not at the 1st video amp -- I eventually found the 36uH coupling inductor to be open. I popped in the closest thing I had - 47uH. Voila, video the whole way through to the DC restorer, and stable DC referenced video at the grid of the CRT. Incidentally, there is an open 500uH inductor in the shunt leg between the 2nd video amplifier and the DC restorer. I haven't replaced it yet - I'm interested to see what difference it makes once I have a picture to look at.

I took a couple of pictures of horizontal lines and vertical fields, with the horizontal and verticals sweeps on the 2nd channel as appropriate. The horizontal hold is rock-solid, but the vertical is extremely touchy. With a little finesse, it pulled it.

Enjoy!

Alex

For fun, here's the output response from a Color Bar pattern. (provided by Comcast in NTSC on Cable 119. Go Figure).

The bottom trace is the detector output, and the top is the CRT Grid.

I'm not sure exactly how much horizontal bandwidth I should expect, but there is exactly ZERO color subcarrier left on that signal by the time it hits the CRT. Those are pretty soft luminance steps, too. And, I don't think thats really color at the detector either. Maybe IF out of alignment?

Alex

...sorry for the 'A Christmas Story' Reference....

With some local help from Wade, we confirmed that this CRT tests good! Also, for what it's worth, it is a replacement tube.

Anyhow, armed with a new 6BG6, we installed the chassis and fired up the set. The HV clearly came up, but the picture was off the screen. A quick tweak of the ion trap brought it into view.

After some vertical size adjustments, the picture fills the majority of the screen. Not Bad! Even after tweaking the vertical linearity control, the linearity leaves a little something to be desired. If I can't tweak it in better, I'll check the bias resistors, caps, etc. in that circuit. Also, the vertical hold is still VERY touchy.

Other than that, the sound doesn't want to tune with the picture, but comes in at the very end of the fine tuning adjustment. Wade suggests replacing all the tube shields may bring things back into alignment.

Lastly, the Width adjustment seems to have more of an effect on contrast than width -- not sure what the deal is. I'll have to trace through the circuit again and make sure I didn't flub a cap placement. But, here's to not having made any GROSSLY serious mistakes in component replacement!

A few screen shots from the local news on WGAL, channel 8. Enjoy. That last picture was shot at 1/60s and shows only a single field, not a full frame. Hence the seemingly large area between scan lines.
Alex

Alex, you may have to tweak up the sound IF to align it with the video IF. Good 'ol RCA and their damnable split sound sets! RCA set are also noteworthy for having rather poor video bandwidth, sub-3Mhz is not uncommon, though I do not have first-hand knowledge of this particular chassis bandwidth performance Don't ever try an put a Col-R-Tel converter on a late 1940's vintage RCA!

Great job getting the set going!

I haven't removed the CRT or the speaker, nor have I made any long wiring harnesses yet, so I put the chassis back in the set
This may be too obvious to mention. Anyway, I was whining in another venue that I wanted to adjust the HV on my RCA CTC-11, but the adjuster was under the chassis and I was too lazy to build extension harnesses. Someone pointed out that you can often turn a chassis sideways and connect everything with the original wiring.

Duh! Time out while I slap my forehead :)

I wouldn't do a lot of soldering like this, but it beats muscling the chassis in and out of the cabinet every time you want to check/adjust some little thing.

The second pic shows a daffy moment 10 years ago when I convinced my wife it would be fun to help hoist the RCA 21T227 cabinet onto my workbench. Can't tell you how many honey-do hours I spent working that one off!

Phil

Thanks for the Tip Phil! Thats a great idea - some of the best ones are really simple!

John - thanks for your encouragement! Without everybody's help, i'd have fuddled around a lot more before getting things right.

Now that the set is 'working', my pace on it will probably slow down a bit, but I'll try to post occasional updates.

Any tips on tuning up an IF stage without a sweep generator? :) I can probably find one to borrow if needed....

Hopefully this set will eventually make it up out of the basement, and into at least occasional use somewhere in the house...
Alex

For the sound IF alignment, you can probably attempt a "by ear" alignment. Tune for best picture, then peak each sound IF and discriminator primary & secondary for best/loudest sound. Make note of the # and direction of turns on each coil you adjust so you can find your way back if need be. I would not recommend this for the video IF alignment.

On John's advice, I executed a 'just tweak it' alignment of the sound IF and discriminator inductors. The result is quite acceptable - except that things only seem to line up on channel 3. So either the tuner or the entire IF chain is still out of alignment. Its good enough for now, since the TV is living it's life w/ an RF output on channel 3 anyhow.

I also picked up a Heathkit IG-57A post marker/sweep generator (minus the attenuator and RF probes - but these can be refabricated), and thanks to a fellow hobbyist, I have attained the schematics and instructions. It actually seems to be in working condition -- the markers are set around 45Mhz IF. However, the marker circuits are pretty simple tuned circuits with crystals for reference in the base of a miller oscillator. I forsee no issues in swapping out the crystals w/ the closest match for 21Mhz IF and adding some capacitance to re-center the tank circuits.

The sweep width and center frequencies are set via a variable saturable inductor. DC current is run through the inductor primary to drive it partially into saturation and lower the effective inductance, changing the center frequency. to get the sweep, some AC current is injected at line freqeuncy to modulate the inductance. I haven't measured much directly, since my scope is only good to 20Mhz, but it looks like its possible to sweep down to the needed frequencies, as-is. I think I'm in good shape, since the Heathkit also has provisions for 10Mhz FM IF.

If and when I get around to it all, I'll post some pictures of the true IF curves Vs Sams.

Well, things are still running well, and I'm getting around to centering the picture.

As it was, it was rotated about 20 degrees CCW, and is off center vertically.

I had previously centered it horizontally using the adjustment on the CRT neck, and was able to bring the picture to correct rotation by loosening the deflection coils and rotating as needed.

However, the picture is still off center vertically 'low'. Does anybody have advice on how to adjust vertical centering? The the adjustment doesn't seem as obvious, and Sams doesn't seem to give any advice.

Right now I'm able to fill the screen by playing with the vertical linearity, but it just stretches things out at the top of the screen.

Any advice?
Thanks!
Alex

There is a centering lever on the side of the magnet assembly.
Up and, down adjustment for horizontal, side by side for vertical.
Loosen the phillips head screw first.
Be sure to tighten when finnished.
Bill Cahill

Thanks Bill!

I got the up and down for horizontal part -- Didn't realize that same adjustment would also do vertical if moved in and out!

Wow...the vertical centering adjustment was very stiff -- I'd have never known it was even there!

Even with the locking screw loosened, I had to use a small screwdriver as a lever to persuade the adjustment to loosen up. I was pretty scared about how much force it took, but eventually it moved and all is well!!

I was able to get it centered, and can now make the vertical linearity look great and still fill the screen. It really made a big difference. The set is very watchable right now.

The sound is relatively decent -- as good as I could get without going through a full IF alignment, but the ratio detector has quite a low SNR. I'm not sure how 'quiet' I should be able to get it. Its very listenable as is, but I don't really know what all I should expect out of it. I'll try to post some new pictures and maybe a test pattern if I can find an easy way to get it from PC to NTSC.

Wow...the vertical centering adjustment was very stiff -- I'd have never known it was even there!

Even with the locking screw loosened, I had to use a small screwdriver as a lever to persuade the adjustment to loosen up. I was pretty scared about how much force it took, but eventually it moved and all is well!!

I was able to get it centered, and can now make the vertical linearity look great and still fill the screen. It really made a big difference. The set is very watchable right now.

The sound is relatively decent -- as good as I could get without going through a full IF alignment, but the ratio detector has quite a low SNR. I'm not sure how 'quiet' I should be able to get it. Its very listenable as is, but I don't really know what all I should expect out of it. I'll try to post some new pictures and maybe a test pattern if I can find an easy way to get it from PC to NTSC.

Actually, that's not a screw adjustment. That tightens the lever when finnished. The lever does all the adjusting. You didn't need to pry it. Merely loosen the screw...
Bill Cahill

I got it -- but the adjustment is just extremely stiff in the 'in/out' direction for vertical. The 'up/down' horizontal adjustment is very fluid. Im not sure whats keeping it from moving freely, but it definitely isn't the locking screw.

At any rate, here are some test patterns. These are aliased no fewer than 3 times.
1)Original to Camera
2)Camera to CRT
3)CRT back to camera

The RCA doesn't get much above 250 lines resolution on the horizontal. It also still has some fairly severe 'ghost' type smear that I haven't been able to tweak out yet.

For comparison, I've shown the same RF feed on Philips that has a good digital comb filter and high horizontal bandwidth - it resolves about 400 lines although hard to tell in this picture.

Finally a couple of 'live' shots. Sorry for the boring subject matter, but I wanted something with high contrast text to show!

First, your width on the right side, that's your right,the tv's left, is too far out.
The horiz. centering is not quite right.
Next, your vertical is stretched. I have the same problem, only worse.
I suspect that if you try to tweak the controls, your vert. will compress, and, you'll have blanking lines on top. I know I do. This is not normal, and, shouldn't be that way.
Next, the resoution, also like mine, isn't right.
It's not properly focussing in the center, and, that's why you only see 250 lines. If anybody has any ideas here, we both need your help.
On mine, all caps, and, electrolytics are new.

Manny resistors in power supply, and, some in vert. circuit are also new.
This has continued to be an on going problem here, as well, except worse than his.
Bill Cahill

Ya, some of these as you note, continue to be minor problems.

But, I think I've about reached the point of decreasing returns. I'm not sure I need this to be perfect, just good enough to be enjoyable to watch.

The vertical isn't stretched too badly after adjustment. The 'height' of the test patern squares is almost unchanged from bottom to top. The width at the extreme right is somewhat compressed, as you note. However, with real programming it is barely noticeable.

The resolution is more than focus for me. The IF section has Sub 3Mhz bandwidth right now. At least I can be 100% sure that there is a steep cutoff before 3.5Mhz, because the color carrier is completely stripped off. (check out the color bar staircase from a few posts ago)

Focus isn't terrible, as the scan lines can be made out with uniform clarity across the entire viewing area. Though, again, I don't have any other B/W sets to really compare with.

Hope we both get a few of these things nailed down!

I figured lots of you guys would have experience with this, so here goes.

Im currently using a VCR to RF modulate for the set, which works great for downconverting all the non VHF channels from analog cable.

But, if I want to watch a DVD (or downconverted HD, or streaming video players) using the VCR as vehicle to RF modulate, i'm having Macrovision Copy Protection Woes, where the macrovision pulses screw with the VCR's AGC circuitry and cause annyoing fading and loss of vertical sync.

Have you guys had luck with external RF modulators for this purpose? I assume these do not usually strip the Macrovision, but leave the TV to still deal with it.
My questions are:
1)Does the AGC in your Vintage TV typically deal with Macrovision gracefully
2)Do the macrovision vertical sync pulses show objectionably in the vertical retrace period?

If results are poor, I could buy a video stabilizer to strip the Macrovision before RF modulating -- but i'm trying to keep the 'number of wires and components' count to a minimum!

Thanks,
Alex

I use a DVD player with an RF Modulator and it usually works very well, some sets handle the Macrovision better than others and some RF Modulators are better than others, you have to experiment a little.
I'm currently using an RCA branded one and it works great.

If you rip and burn a DVD on your PC using DVD Shrink or something similar it leaves off the Macrovision Flag and that usually eliminates a lot of the lines and junk at the top of the screen.

I've also burned Public Domain videos from the Prelinger Archives to DVD and they work very well.

Thanks Eric,

I'll try an off the shelf RF modulator - I can always add a video stabilizer if needed.

Right now, the majority of my movies come from a Roku Streaming Video player, which also inserts macrovisoin, which surprised me.

I am curious to bypass the RF and IF stages and apply baseband video directly to the video amp section. Just wonder what the set would look like with better video bandwidth.

Sometime in the past (I think it was on a CT-100 restoration site) I remember somebody had a schematic for an add on circuit to do just this. Does this ring a bell with anybody? I tried a quick google search but couldn't come across it.

I could probably come up with something reasonably easily, but this would save some time, and might make a fun weekend project sometime!

Alex

Not sure about your set, but on both my Philco and Sylvania Halolight I was able to inject a composite signal directly to the video amp tube's grid. Made a fantastic picture bypassing all the RF/IF stages, but you shouldn't need any add on circuits to do it. Just make sure you use a shielded cable to make the connection, to avoid interference. Same thing can be done with the audio stage, but make sure you make the connection so that the volume still functions.
I know some 'purists' don't approve :nono:, but my Philco has 2 RCA jacks on the back, and I didn't have to cut anything to do it- the round heat holes were the perfect size for mounting the jacks!
Try it, you might be surprized at the picture you see. :thmbsp:

Folks, DON'T try that at home with a hot-chassis TV, though.

That wouldn't be good, no.